The present invention relates to an improved system for proving a densitometer, such as a densitometer of the type used in conjunction with pipelines for natural gas liquids.
In pipeline operations the accuracy of densitometers can be critically important. Densitometers are typically used in conjunction with flow meters to measure mass flow into and out of a pipeline, and erroneous densitometer readings can have serious economic consequences. For example, if densities and therefore mass flows into and out of a pipeline are not measured accurately, significant errors resulting in significant losses can result in favor of either a pipeline operator or a pipeline user. For these reasons, a need exists for proving densitometers with high accuracy.
In the past, densitometers have been conventionally proved (i.e., their linearity checked) by calibrating the densitometer with low vapor pressure substances such as air, water, heptane, and the like. In the past, it has often been assumed that if a densitometer is linear for air and water, it is linear for materials with specific gravities between air and water.